1. Field of the Invention
Within the field of interferometry, particularly for measuring manufactured components, optical probes position beams for scanning surfaces of the components. The probes direct measuring beams to points on the component surfaces, and relative motion between the probes and the components provides for measuring areas of the component surfaces.
2. Description of Related Art
Optical probes provide a non-contact means for surface form and geometrical measurement of test objects, particularly manufactured components. Typically, measuring beams directed from optical probes retroreflect from component surfaces and are returned for analysis by an interferometer. Conventional practice locates the optical probes within a test arm of the interferometer, and measuring beams returned from the test arm are combined with reference beams returned from a reference arm to compare their lengths of optical travel.
Relative motion between the optical probes and the test objects scans the measuring beam across the surfaces of test objects to acquire information about different points on the surfaces. The relative motion, which can involve rotation or translation, tracks paths that are parallel to the surfaces so that changes in length differences between measuring and reference beams can be interpreted as deviations from the expected form of the component surfaces.
For measuring rotational surfaces (i.e., surfaces of revolution), the optical probe can be translated and the test object can be rotated. The measuring beam from the optical probe is focused onto the test surface at a given radius with respect to the center of rotation of the test object. Rotation of the test object enables the measuring beam to scan a circumference of the test object. Subsequent translations of the optical probe in an axial plane of test object rotation allow the remainder of the rotational surface to be scanned.
The measurement of compound surfaces of test objects presents special challenges, particularly when the measurements are intended for deriving relative information between the compound surfaces. For example, compound rotational surfaces of test objects can be compared for concentricity and runout. An optical probe effective for these purposes is disclosed in co-assigned U.S. patent application Ser. No. 10/277,798, entitled “Two-wavelength Confocal Interferometer for Measuring Multiple Surfaces”, which is hereby incorporated by reference.
The disclosed optical probe splits a measuring beam into two measuring beam portions that are directed from the probe to different points of focus through different angles of inclination normal to two compound surfaces of a test object. Both beam portions are focused by the same focusing optics prior to their split. However, a beamsplitter reflects one of the converging beam portions in a first direction from the probe. A prism deflects the remaining converging beam portion in a second direction from the probe. The probe geometry and scan path are chosen such that only one beam is focused onto the surface being measured. Confocal imaging then ensures that signal from only this beam is obtained.
Both the relative orientation and the number of compound surfaces requiring measurement can vary among test objects. Constructing optical probes unique to each such situation is expensive and requires remounting and re-calibrating probes to measure the differently oriented compound surfaces.